Structured plate-like glass element and process for the production thereof

ABSTRACT

A method includes: providing a plate-like glass element having side faces and an ultrashort pulse laser having a laser beam; directing the laser beam onto one of the side faces; concentrating the laser beam by focusing optics to form an elongated focus in the glass element; producing a filament-shaped flaw in a volume of the glass element by a radiated-in energy of the laser beam, a longitudinal direction of which runs transverse to one of the side faces, and the ultrashort pulse laser radiates in a pulse or a pulse packet having at least two successive laser pulses to produce the filament-shaped flaw; widening the filament-shaped flaw to form a channel by exposing the glass element to an etching including an etching medium which removes glass at a rate of less than 8 μm per hour; and introducing rounded, hemispherical depressions in a wall of the channel by the etching.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. patent application Ser. No. 15/882,187,entitled “STRUCTURED PLATE-LIKE GLASS ELEMENT AND PROCESS FOR THEPRODUCTION THEREOF,” filed Jan. 29, 2018, which is incorporated hereinby reference. U.S. patent application Ser. No. 15/882,187 is anon-provisional application based upon U.S. provisional patentapplication Ser. No. 62/451,117, entitled “STRUCTURED PLATE-LIKE GLASSELEMENT AND PROCESS FOR THE PRODUCTION THEREOF”, filed Jan. 27, 2017,which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to the structuring of glasses,and more particularly, to a laser-based process for structuring glass,and also the glass elements which can be produced thereby.

2. Description of the Related Art

The precise structuring of transparent, opaque and nontransparentglasses is of great interest in many fields of application. Here,precisions in the region of a few microns are required. The structuringrelates to holes (round and angular), cavities, channels or any freeshapes. In order to be used in a wide range of applications, the workingshould leave behind no damage, residues or stresses in the outer regionor volume of the substrate. Furthermore, the process should allow a veryefficient manufacturing process. Various methods can be employed forproducing holes. Apart from sandblasting through appropriate masks,ultrasonic vibratory lapping is an established process. However, bothmethods are, due to their scale, restricted to small structures whichare typically at about 400 μm in the case of ultrasonic vibratorylapping and at a minimum of 100 μm in the case of sandblasting. Owing tothe mechanical removal of material, stresses in the glass, associatedwith flaking at the peripheral region of the hole, are produced in thecase of sandblasting. Both processes are fundamentally unsuitable forthe structuring of thin glasses.

In recent times, many laser sources have been used for the structuringof various materials. Here, virtually all known laser sources, e.g. CO₂or CO lasers, diode-pumped ns, ps, and fs solid-state lasers having aninfrared (e.g. 1064 nm), green (532 nm) and UV (365 nm) wavelength, havebeen used. Excimer lasers, which work at extremely short wavelengths(e.g. 193 nm, 248 nm), are also used for processing. The working ofglasses is particularly demanding since they generally have a lowthermal conductivity and a high susceptibility to fracture. All laserablation processes therefore lead to more or less strong thermalstressing or heat input, which does decrease at shorter wavelengths andshorter pulse lengths but sometimes still leads to critical stressesthrough to microcracks and deformations in the peripheral region of theholes. At the same time, clearly measurable roughnesses are stillproduced on the hole walls when this process is used since all laserprocesses ablate in a cluster-like manner, i.e. the respective clustersize determines the residual roughness of the walls.

To produce very small structures in the surfaces, the laser ablationprocess is used. A disadvantage here is that deep structures can beachieved only with multiple passes over the work piece to be processed.The processing time is correspondingly slow. The process is therefore ofonly limited suitability for use in industrial manufacture. This appliesparticularly when through-openings or structures in general which extendfrom one side face to the opposite side face are to be introduced inglasses. The walls of such structures, e.g. of furrows, also have aninclination, i.e. are not perpendicular.

A further problem is, especially in the structuring of glasses asbrittle-hard materials, that the structures introduced can significantlydecrease the strength under flexural stresses. This applies particularlywhen the structures produced form part of an edge or an opening goingthrough the glass.

What is needed in the art is a glass element having fine structureswhich extend between the side faces of the glass element but reduce thestrength very little or even increase the strength.

SUMMARY OF THE INVENTION

The invention accordingly provides a plate-like or tabular glass elementhaving two opposite side faces, generally running parallel to oneanother, and a channel which has been introduced into the glass of theglass element and joins the two side faces and opens into the side facesand has a rounded wall and a transverse dimension of less than 100 μm,for example less than 70 μm. The longitudinal direction of the channelruns transverse to the side faces. Here, the wall of the channel has aplurality of rounded, substantially hemispherical depressions. Thelongitudinal direction of the channel particularly may run perpendicularto the side faces, or accordingly parallel to the normal to the sidefaces. The channel opens into the side faces.

Such a glass element is produced by a laser-based process. The processof the invention for producing the plate-like glass element is based on:

-   -   the laser beam of an ultrashort pulse laser being directed onto        one of the side faces of the glass element and concentrated by        focusing optics to form an elongated focus in the glass element,        where    -   a filament-shaped flaw is produced in the volume of the glass        element by the radiated-in energy of the laser beam, the        longitudinal direction of which runs transverse to the side        face, in particular perpendicular to the side face, and the        ultrashort pulse laser radiates in a pulse or a pulse packet        having at least two successive laser pulses to produce a        filament-shaped flaw and, after introduction of the        filament-shaped flaw,    -   the glass element is exposed to an etching medium which removes        glass of the glass element at a removal rate of less than 15 μm,        for example less than 10 μm, for example less than 8 μm per hour        and    -   the filament-shaped flaw widens to form a channel which        consequently lies with its longitudinal direction in the        direction of the longitudinal direction of the filament shaped        flow and    -   introduces rounded, substantially hemispherical depressions in        the wall of the channel.

In some exemplary embodiments provided according to the invention, amethod for producing a plate-like glass element includes the steps of:providing the plate-like glass element having a pair of side faces andan ultrashort pulse laser having a laser beam and focusing optics;directing the laser beam of the ultrashort pulse laser onto one of theside faces of the glass element; concentrating the laser beam by thefocusing optics to form an elongated focus in the glass element;producing at least one filament-shaped flaw in a volume of the glasselement by a radiated-in energy of the laser beam, a longitudinaldirection of which runs transverse to the one side face of the sidefaces, and the ultrashort pulse laser radiates in a pulse or a pulsepacket having at least two successive laser pulses to produce the atleast one filament-shaped flaw, and, after introduction of the at leastone filament-shaped flaw; widening the at least one filament-shaped flawto form at least one channel by exposing the glass element to an etchingprocess which includes an etching medium which removes a glass of theglass element at a removal rate of less than 8 μm per hour; andintroducing rounded, substantially hemispherical depressions in a wallof the at least one channel by the etching process.

The pulse energy of the individual pulse is selected so that it is belowthe ablation threshold of the glass, so that the laser light canpenetrate into the glass and the laser energy is not consumed at thesurface by the ablation process.

The particular structuring of the lateral surface of the channels withsubstantially hemispherical depressions results in a number ofadvantages. Firstly, the rounded structures may represent a particularlyadvantageous shape in order to dissipate tensile stresses occurring onthe surface down to the lowest point of the surface, namely the lowestpoints of the substantially hemispherical depressions. This effectivelysuppresses crack growth at possible defects in the surface.

In particular, parts of the glass element 1 can also be separated off byintroduction of the channels when these are produced next to one anotherand edges, in particular also internal edges of openings, can thus beproduced. Such openings may have a transverse dimension of at least 200μm, for example at least 300 μm.

The substantially hemispherical depressions form, in particular, when aslow etching process is carried out. The abovementioned low etching rateof less than 15 μm per hour is therefore provided. Furthermore, thesubstantially hemispherical depressions are presumably brought about bystructures which occur on introduction of the filament-shaped flaws. Theburst mode with the inward radiation of a pulse packet can be used toachieve elongated, uniform flaws.

As etching medium, particular preference is given to an etchingsolution. In this embodiment, etching is thus carried outwet-chemically. This may be advantageous in order to remove glassconstituents from the surface during etching. As etching solution, it ispossible to use both acidic and alkaline solutions. As acidic etchingmedia, HF, HCl, H₂SO₄, ammonium bifluoride, HNO₃ solutions or mixturesof these acids are particularly suitable. For basic etching media, KOHor NaOH solutions may be used. Greater rates of removal of material cantypically be achieved using acidic etching solutions. However, basicsolutions can be used, especially since only a slow removal of materialis sought in any case.

Furthermore, etching can be carried out in a temperature range from 40°C. to 150° C., for example from 50° to 120°, for example up to 100° C.

In general, siliceous glasses having a low alkali metal content areparticularly suitable for the structuring according to the invention.Excessively high alkali metal contents make etching more difficult. Oneembodiment of the invention therefore provides for the glass of theglass element to be a silicate glass having a content of alkali metaloxides of less than 17 per cent by weight.

In the burst operating mode provided for the invention, the laser energyis not supplied as a single pulse but as a sequence of pulses whichfollow one another at short intervals and together form a pulse packet,known as a burst. Such a pulse packet typically has somewhat more energythan a single pulse in the conventional single-shot mode of operation.However, the pulses of a burst themselves contain significantly lessenergy than a single pulse. With regard to pulses within a burst, thepulse energies can be set flexibly, in particular so that the pulseenergies either remain essentially constant or so that the pulseenergies increase or so that the pulse energies decrease. In any case,the surface structure according to the invention with a channel havingthe concave, rounded pits or the substantially hemispherical depressionsis obtained particularly when the filament-shaped flaws are introducedby laser pulses in the burst mode.

One suitable laser source according to the present invention is aneodymium-doped yttrium-aluminum garnet laser having a wavelength of1064 nanometers.

The laser source produces, for example, an initial beam having a (1/e²)diameter of 12 mm; a biconvex lens having a focal length of 16 mm can beused as optics. To produce the initial beam, it is optionally possibleto use suitable beam-forming optics, for example a Galileo telescope.

The laser source operates, with a repetition rate in the range from 1kHz to 1000 kHz, for example from 2 kHz to 100 kHz, for example from 3kHz to 200 kHz.

The repetition rate and/or the scanning rate can be selected so that thedesired distance between neighboring filament-shaped flaws is achieved.

A suitable pulse duration of a laser pulse can be in the range of lessthan 100 picoseconds, for example than 20 picoseconds.

The typical power of the laser source can be in the range from 20 to 300watt. In order to achieve the filament-shaped flaws, a pulse energy inthe burst of more than 400 microjoule is used in an embodiment of theinvention; a total burst energy of more than 500 microjoule may be moreadvantageous.

When the ultrashort pulse laser is operated in the burst mode, therepetition rate is the rate of repetition of the release of bursts. Thepulse duration depends mainly on whether a laser is operated insingle-pulse operation or in the burst mode. The pulses within a bursttypically have a similar pulse length as a pulse in single-pulseoperation. The burst frequency can be in the range from 15 MHz to 90MHz, for example in the range from 20 MHz to 85 MHz, and is for example50 MHz and the number of pulses in the burst can be in the range from 1to 10 pulses, e.g. 6 pulses.

In order to achieve opening of the channels into both side faces, thefilament-shaped flaw can go essentially completely across the glasselement, but it is not necessary for a flaw going all the way through tobe observed. The filament-shaped flaw can, for instance, also be asequence of local defects arranged in succession. In order to produce achannel running through the glass element 2, however, relatively thinglass elements are generally suitable in any case. The thickness rangefor the glass elements may be from 30 microns to 3 millimeters.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is an apparatus for laser working of the glass elements aspreparation for subsequent etching;

FIG. 2 illustrates a glass element with introduced filament-shapedflaws;

FIG. 3 illustrates the glass element with channels introduced along thefilament-shaped flaws;

FIG. 4 illustrates the glass element after a part has been separatedoff;

FIG. 5 illustrates a variant of the glass element shown in FIG. 4;

FIG. 6 and FIG. 7 illustrate electron micrographs of an edge of a glasselement in different enlargements;

FIG. 8 and FIG. 9 illustrate electron micrographs of channels which havebeen introduced using different laser parameters;

FIG. 10, FIG. 11, and FIG. 12 illustrate process steps according to anembodiment of the invention with the aid of cross-sectional views;

FIG. 13 is a graph of the angle of taper of the channels as a functionof the etching rate;

FIG. 14 illustrates two electron micrographs of the openings ofchannels;

FIG. 15 illustrates a glass element with two openings separated by aweb, in plan view of a side face;

FIG. 16 illustrates another embodiment having a plurality of websrunning parallel to one another;

FIG. 17 illustrates another embodiment with webs which are free at oneend;

FIG. 18 and FIG. 19 are electron micrographs of an edge of a glasselement in different enlargements;

FIG. 20 illustrates a glass element with a web;

FIG. 21 illustrates a glass element with several structures connected bywebs; and

FIG. 22 illustrates a glass element which is prepared for detachinginner parts.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate embodiments of the invention and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a working example of a laser processing apparatus 20, fromwhich filament-shaped flaws 32 can be introduced into a glass element 1in order to introduce channels at the positions of the filament-shapedflaws 32 in a subsequent etching process. The apparatus 20 includes anultrashort pulse laser 30 having preceding focusing optics 23 and apositioning device 17. The positioning device 17 enables the point ofimpingement 73 of the laser beam 27 of the ultrashort pulse laser 30 tobe positioned laterally on the side face 2 of a plate-like glass element1 to be worked. In the example depicted, the positioning device 17comprises an x-y table on which a side face 3 of the glass element 1rests. However, as an alternative or in addition, it is also possible tomake the optics mobile in order to move the laser beam 27 so that thepoint of impingement 32 of the laser beam 27 can be moved with the glasselement 1 remaining fixed.

The focusing optics 23 then focus the laser beam 27 to form a focuswhich is elongated in the direction of the beam, i.e. accordinglytransverse, in particular perpendicular, to the irradiated side face 2.Such a focus can, for example, be produced by way of a conical lens(known as an axikon) or a lens having great spherical aberration. Thecontrol of the positioning device 17 and of the ultrashort pulse laser30 may be effected by way of a programmed computer 15. In this way,predetermined patterns of filament-shaped flaws 32 distributed laterallyalong the side face 2 can be produced, in particular by input ofpositional data, for example from a file or via a network.

According to one embodiment, the following parameters can be used forthe laser beam:

The wavelength of the laser beam is 1064 nm, typical for a YAG laser. Alaser beam having an initial beam diameter of 12 mm is produced, andthis is then focused by way of optics in the form of a biconvex lenshaving a focal length of 16 mm. The pulse duration of the ultrashortpulse laser is less than 20 ps, for example about 10 ps. The pulses areemitted in bursts of 2 or more, for example 4 or more pulses. The burstfrequency is 12-48 ns, e.g. about 20 ns, the pulse energy is at least200 microjoule and the burst energy is accordingly at least 400 microjoule.

Subsequently, after introduction of one or in particular more than onefilament-shaped flaw(s) 32, the glass element 1 is taken out and placedin an etching bath where, in a slow etching process, glass is removedalong the filament-shaped flaws 32 so that a channel is introduced intothe glass element 1 at the position of such a flaw 32.

A basic etching bath may have a pH of >12, for example a KOH solutionhaving a concentration of >4 mol/l, for example >5 mol/l, for example >6mol/l, but <30 mol/l. Etching is, in one embodiment of the invention,carried out at a temperature of the etching bath of >70° C., forexample >80° C., or >90° C., irrespective of the etching medium used.

FIG. 2 shows, in plan view onto a side face 2, a glass element 1 havinga plurality of filament-shaped flaws 32 which are arranged in aparticular pattern as can be inscribed in the glass element 1 by theabove-described computer-controlled actuation of the positioning device17 and the ultrashort pulse laser 30. The filament-shaped flaws 32 mayhave here been introduced, by way of example, along a prescribed path inthe form of a closed rectangular line into the glass element 1. Thecorners of the line can also be slightly rounded. A person skilled inthe art will be able to see that not only rectangular paths but alsopaths of any shape can be produced by way of the process.

FIG. 3 shows the glass element 1 after a subsequent etching step.Instead of the filament-shaped flaws 32, channels 5 which are arrangednext to one another along the prescribed path and form a row are nowpresent. The glass element 1 is shown as a hatched area in order todistinguish the element from openings, e.g. the channels 5 in thedrawing.

The channels 5 which have been introduced and are arranged next to oneanother to form a row along the path over which the laser travels cannow serve as predetermined fracture positions in order to separate offpart of the glass element 1, or the glass element 1, along this path.

FIG. 4 shows the glass element after parting along the path. Since thechannels were arranged along a rectangular, closed parting line, aninner part is detached and an opening 13 is created in the glass element1 by the parting operation.

Quite generally, without being restricted to the specific workingexample, a plate-like glass element 1 having a channel 5 which is openat the side and forms part of an edge 10 of the glass element 1 isformed by parting along a line running through one or more channels 5.

Furthermore, as shown in FIG. 3, glass material was still presentbetween the channels 5. Accordingly, inner part and surrounding glasselement 1 were still joined to one another after etching. The finalparting operation can then be performed, for example, by breaking. Owingto the perforation created by the channels 5 arranged next to oneanother, the glass element 1 breaks along the path of the channels 5arranged in a row. In general, without being restricted to the exampleshown, an edge 10 in which, as depicted in FIG. 4, flat edge sections 11extend between the channels 5 is created in this way. The flat edgesections 11 are formed on fracture of the glass between the channels 5.

In order to detach an inner part and/or produce an opening 13 in a glasselement 1, a variant of the above-described method can be suitable. Thisembodiment of the invention is based on the diameter of the channels 5being increased by etching to such an extent that the glass between thechannels 5 is removed and the channels 5 join.

A glass element 1 in which the channels 5 have joined at the sides as aresult of etching is shown in FIG. 5. As in the example of FIG. 4, thechannels 5 are arranged next to one another in a row along a closedpath. Accordingly, an opening 13 and a complementary inner part are inturn produced by the detaching operation. In the example depicted, theinner part 9 has been separated off but is still arranged in the opening13.

FIG. 2 to FIG. 5 are examples of an embodiment of the inventionaccording to which an edge 10 of the glass element 1 which has aplurality of channels 5 which run parallel next to one another and areopen at the sides is created.

Furthermore, all these examples are based on an embodiment of theprocess of the invention in which

-   -   the point of impingement 73 of the laser beam 27 on the glass        element 1 is conveyed along a prescribed path and    -   a plurality of filament-shaped flaws 32 located next to one        another on the path are introduced into the glass element 1 and    -   a plurality of channels 5 located next to one another are        subsequently introduced by etching into the glass element 1, and    -   the glass element 2 is then parted along the path so as to form        an edge 10 having channels 5 which are open at the side.

The channels 5 generally have a tubular cylindrical basic shape, or aretubular with a cylindrical wall. Here, a slight taper from the openingat the side face to the middle of the glass element 1 can be present.When the generally cylindrical channels 5 are joined in the course ofwidening during the etching operation, ridges are formed at the abuttingpositions. In general, without being restricted to the example of FIG.5, one embodiment of the invention provides for the channels 5 to adjoinone another so as to form ridges 52 which are located between thechannels 5 and run parallel to the longitudinal direction 51 of thechannels 5.

These ridges or ribs accordingly run parallel to the longitudinaldirection of the channels and can therefore be seen only as serrationsor tooth-like elements at the position of the transition region betweenneighbouring channels 5 in the depiction of FIG. 5.

FIG. 6 and FIG. 7 show electron micrographs of the edge 10 of a glasselement 1 which has been worked according to the invention. Here, FIG. 7was taken at a greater enlargement. As in the examples of FIG. 4 andFIG. 5, the edge 10 has a plurality of channels 5 which run parallel toone another and are open at the side. In the depiction of FIG. 6 in planview onto the edge 10, it can be seen that the longitudinal direction 51extends transversely, in particular perpendicularly, to the side faces2, 3. However, in the section depicted in FIG. 6, only the transition ofthe edge 10 to one of the side faces, here denoted as side face 3, is tobe seen. In a manner analogous to the example of FIG. 3, the edge 10 hasflat edge sections 11 in addition to the channels 5 open at the side.The edge 10 was thus produced by breaking along the parting line whichhas been weakened by the channels 5.

The spacing of the channels 5 is relatively large at about 50 μm in thisexample. The spacing can also be made smaller, especially in the casewhere the channels 5 go directly into one another without flat edgesections 11. In general, the spacing of the channels (also referred toas “pitch”) may be in the range from 3 to 70 microns. This spacing ismeasured from the middle to the middle of the channels. The transversedimension, or the diameter of the channels 5, is, as indicated above,less than 100 microns. The diameter may be in a similar region to thespacing of the channels 5. Without being restricted to the examplesdescribed here, the diameter may be in the range from 3 microns to 50microns. In the example of FIG. 6 and FIG. 7, the diameter is about 30microns.

The depth of the substantially hemispherical depressions 7 is typicallyless than 5 μm, at transverse dimensions of typically 5-20 μm.

It can be seen that the area of the edge 10 is greater than the area ofa flat edge as a result of channels 5 having an approximatelysemicircular cross section through the lateral opening. If the channels5 were to adjoin one another directly and have a precisely semicircularcross section, the length of the edge line parallel to the side faces 2,3 would be greater by a factor of π/2 than the edge line of a smoothedge. The increases in the area which can be achieved by the process ofthe invention are somewhat smaller and are generally in the region offrom 10 to 40 per cent. According to one aspect of the invention, aplate-like glass element 1 having two opposite side faces 2, 3 and anedge 10, where the edge has a plurality of channels 5 which run parallelto one another and are open at the side and have a rounded wall 54 and atransverse dimension of less than 200 μm and whose longitudinaldirection 51 runs transverse, e.g. perpendicular, to the side faces 2, 3and which also end at the side faces 2, 3, or open into these, with thesurface area of the edge 10 being increased by a factor of from 1.1 to1.4 by the channels 5 compared to a smooth edge face without channels 5,is therefore provided. The edge 10 can be an outer edge or else, as inthe examples of FIG. 4 and FIG. 5, an inner edge which delimits anopening 13. Thus, openings having a transverse dimension of at least 200μm, for example also more than 300 μm, may be produced. The transversedimension here is the longest lateral extension of the opening. In thecase of a circular opening, the transverse dimension thereof is given bythe diameter.

This increase in the surface area gives a comparatively fracture-stableedge under flexural stresses, which is surprising in so far as thefracture probability normally correlates with the surface area. Thestructures projecting beyond the rounded channel probably lead todefects on these projected structures (ridges or flat edge sections) notbeing able to propagate far. Crack propagation is thus suppressed by thestructuring of the edge 11.

This effect is reinforced further by the inventive fine structure of thechannels 5 which is explained in more detail below. In FIG. 6 and FIG.7, the fine structure of the channels 5 in the form of substantiallyhemispherical or rounded, cap-like depressions 7 can clearly be seen. Asa result of the slow etching process, the substantially hemisphericaldepressions 7 adjoin one another, with the abutting concave roundings ofthe depressions 7 forming ridges 70.

Furthermore, it can be seen that the ridges 70 form polygonal delimitinglines 71 of the depressions 7 when looked at in plan view onto thedepressions 7. Here, the average number of the corners 72 of thedelimiting lines 71 of the depressions 7 may also be less than eight,for example less than seven. The latter feature is obtained when theregions included by most of the substantially hemispherical depressionsare convex in the mathematical sense.

The ridges 70 of the channel 5 shown in FIG. 7 are very narrow, andthere are no discernible regions in which the concave curvatures of thedepressions 7 go over into one another via a convexly domed region onthe ridge 70. The structure of the channels 5 can therefore, accordingto an embodiment of the invention, also be described by the proportionby area of convex regions in a channel 5 being less than 5%, e.g. lessthan 2%.

The glass element 1 of the example shown in FIG. 5 and FIG. 6 is asiliceous glass having a low alkali metal content, specifically aborosilicate glass having a coefficient of thermal expansion of 3.3*10⁻⁶K⁻¹. As borosilicate glass, a glass may have the following composition:

Composition (% by weight) SiO₂ 63-83 Al₂O₃ 0-7 B₂O₃  5-18 Li₂O + Na₂O +K₂O  4-14 MgO + CaO + SrO + BaO + ZnO  0-10 TiO₂ + ZrO₂ 0-3 P₂O₅ 0-2

FIG. 8 and FIG. 9 show electron micrographs of channels which have beenintroduced into a borosilicate glass marketed under the tradename D263®by Schott. Different laser parameters were used here. In the example ofFIG. 8, a burst having 8 individual pulses was used, with the repetitionrate of the laser being 100 kHz. In the example shown in FIG. 9, ahigher repetition rate of 200 kHz was used, but a burst having only twoindividual pulses was employed. In each case, however, only a singleburst was radiated in for each channel 5. The channels 5 were thenetched in a KOH solution at 80° C. for a time of 8 hours. The structureof the channels 5 is similar, with the substantially hemisphericaldepressions 7 appearing even more concave because of the smallerdiameter compared to the example of FIG. 6 and FIG. 7. On furtheretching, the structure approaches that of FIG. 6 and FIG. 7.

A further glass from the class of low-alkali siliceous glasses which iswell suited to the process of the invention is an alkali metal-freealuminasilicate glass. A glass may have the following composition:

Composition (% by weight) SiO₂ 50-75  Al₂O₃ 7-25 B₂O₃ 0-20 Li₂O + Na₂O +K₂O  0-0.1 MgO + CaO + SrO + BaO + ZnO 5-25 TiO₂ + ZrO₂ 0-10 P₂O₅ 0-5 

Without being restricted to the abovementioned compositions, the glassesmay have basicities in the range from 0.45 to 0.55, for example in therange from 0.48 to 0.54. This makes the glasses suitable for slow,controlled etching using basic etching media, but etching using acidicetching media also remains possible.

The embodiments described hitherto can have the disadvantage that notonly the filament-shaped flaw but also both side faces 2, 3 of the glasselement 1 are etched. Although the etching rate here is lower thanwithin the channels 5, the decrease in thickness can nevertheless beundesirable. It may also be desirable not to alter the surface of theglass by way of the etching process. To avoid these disadvantages, afurther embodiment of the invention provides for the surface of theglass element 1 to be covered in a first step by a polymer coating (forexample a film or a surface coating) which is removed locally onintroduction of the laser light. Thus, the polymer coating remains inthe regions which surround the point of impingement of the laser andthus also the filament-shaped flaw and thus protects these regions ofthe side faces during subsequent etching.

The process and the glass element obtained are depicted in FIG. 10 toFIG. 12.

This embodiment of the invention is thus based on at least one side face2, 3, for example both side faces 2, 3 as shown in FIG. 10, beingprovided with a polymer layer 35 before irradiation with the laser beam27.

A glass element 1 as is shown schematically in FIG. 12 is obtained. Ifthe diameter of the channel 5 is smaller than the diameter of theablated opening 36 in the polymer layer 35, a glass element 1 in whichthe channel 5 is surrounded by a region having an etched surface isobtained, with this etched region on the side face once again beingsurrounded by an unetched region.

It can be seen even from FIG. 7 that the channels 5 which can beproduced according to the invention have a substantially cylindricalbasic shape. Associated therewith, angles of taper approximating 90° canbe produced. The angle of taper of a channel 5 is the angle of the wallof the channel relative to the respective side face 2, 3. This anglecan, inter alia, vary locally owing to the fine structure of thechannels with the substantially hemispherical depressions 7 and istherefore determined by averaging. Simple averaging can be determined bycalculation of the angle of taper from the aspect ratio of the channel5. The aspect ratio is the ratio of the depth of a channel to thesmallest channel diameter. In the case of an open channel 5 as isprovided according to the invention, the half channel length can forthis purpose be divided by the difference between hole diameter at theside face to hole diameter at half the length of the channel. FIG. 13shows measured values of the angle of taper in the case of etching byway of sodium hydroxide solution as a function of the etching rate. Thesmaller the etching rate, the more closely does the angle of taperapproximate a right angle. In the case of the etching rate of less than8 um per hour as employed according to the invention, the angle of taperis in this example greater than 87°. The angle of taper can beinfluenced not only by the etching rate but also by the type of glassand the etching medium. In general, however, the angle of taper of theat least one channel 5 deviates from a right angle by less than 5°, forexample less than 3°, or even less than 1°, according to an embodimentof the invention.

A very circular cross section superimposed by small deviations from thecircular shape as a result of the substantially hemisphericaldepressions 7 can also be achieved by way of the process of theinvention. FIG. 14 shows two electron micrographs of the opening 6 ofchannels 5 which have been etched by way of an NaOH solution into theglass element 1. As can be seen, the openings 6 of the channels 5 arevirtually circular. As a measure of the circulatrity, a roundnessdeviation can be defined. This is the ratio of circumference of theopening 6 to the circumference of a circle having the same enclosedarea. A perfectly circular channel would accordingly have a roundnessdeviation of 1.0. It has been found that, in general, a roundnessdeviation of less than 1.15 is achieved by way of the process of theinvention, both on etching with HF and also with KOH or NaOH, despitethe substantially hemispherical depressions 7. The roundness deviationcan also be determined for channels 5 which are open at the side and arepart of an edge 10 by, for example, calculating this value in ananalogous manner for a circular segment.

The invention is suitable, inter alia, for producing interposers forelectronic or microfluidic applications. For electronic applications,the channels 5 or openings having inner edges according to the inventioncan be filled with a conductive material in order to produce electriccontacts from one side face to the other side face. Likewise, thechannels 5 or larger openings produced by the channels 5 can serve forthe conduction of fluids. If material is introduced into the channels 5,for instance to produce electric conduits through the glass element, thesubstantially hemispherical depressions 7 offer the advantage that thismaterial can anchor readily in the channels 7. In the conduction offluids, the depressions 7 can, on the other hand, reduce the flowresistance. Suitable applications are MEMS components. Here, particularmention may be made of a pressure sensor in which the glass element isfastened to a cap which deforms under the action of pressure. Here,openings for leading electric contacts to the cap and, particularly fora differential or relative pressure measurement, to allow pressureequilibration to the gas volume enclosed in the cap can be provided.Such a pressure sensor can measure capacitively, piezoresistively orresistively. In a resistive measurement, electric resistance layerswhich are connected to form a Wheatstone bridge can be provided in thecap. The voltage measured at the bridge is then proportional to thepressure-related deformation of the membrane.

A pressure sensor comprising a glass element according to the inventioncan, inter alia, be used in the following applications: a fuel pressuresensor in injection systems, an oil pressure sensor in gearboxes, asensor in an airbag or for air pressure, e.g. for altitude measurements,a tyre pressure sensor.

If the spacing of the filament-shaped flaws is small, the channels 5 canquickly go over into one another during etching. The longer the etchingprocess continues, the more do the structures produced by the channels 5flatten. In contrast, the structure of the adjoining substantiallyhemispherical depressions 7 is retained. A further embodiment of theinvention accordingly provides a plate-like glass element 1 having twoopposite side faces 2, 3 and an edge 10 joining the two side faces 2, 3,with the edge 10 having a plurality of adjoining, rounded, substantiallyhemispherical depressions 7. Regardless of whether channels 5 canadditionally be discerned, the lateral dimension or average transversedimension of the depressions 7 is typically on average less than thedepth thereof. The depressions 7 thus represents flat pans.

In order to obtain an essentially flat edge 10 without visible channels5 running next to one another, a spacing of the filament-shaped flaws ofless than 6 μm, e.g. less than 5 μm, can be used. An embodiment of theinvention accordingly provides a process for producing a plate-likeglass element 1 having a structured edge 10, wherein

-   -   the laser beam 27 of the ultrashort pulse laser 30 is directed        onto one of the side faces 2, 3 of the glass element 1 and        concentrated by focusing optics 23 to form an elongated focus in        the glass element 1, where    -   the point of the impingement 73 of the laser beam 27 on the        glass element 1 is moved along a prescribed path and    -   a plurality of filament-shaped flaws 32 located next to one        another on the path at a spacing of not more than 6 μm, the        longitudinal direction of which runs transverse to the side face        2, 3, in particular perpendicular to the side face 2, 3, are        introduced by way of the laser beam and    -   the glass element 1 is exposed to an etching medium 33 which        removes the glass of the glass element 1 at a removal rate of        less than 8 μm per hour and    -   widens the filament-shaped flaws 32 to form channels 5 and the        diameter of the channels 5 is increased by the etching to such        an extent that the glass between the channels 5 is removed and        the channels 5 join to form an edge 10 which divides the glass        element 1.

A particular aspect of the invention when the process is used forseparating off parts, in particular detaching inner parts and thusproducing openings 13, is that very thin webs are produced as glassstructures by two edges which run close to one another and have theinventive structure being introduced. FIG. 15 shows an example of this.

An embodiment of the invention therefore provides a plate-like glasselement 1 which has a thickness in the range from 30 microns to 3millimetres and has two opposite side faces 2, 3, wherein the contour ofthe glass element 1 comprises an elongated web 40 whose length 41 is atleast five times, for example at least ten times, greater than itswidth, with length and width in each case being measured in a directionalong a side face, and the edges 10 of the web 40 running next to oneanother each having a plurality of adjoining, rounded, substantiallyhemispherical depressions 7. The web 40 may be produced by separatingoff parts at the edges 40, using the above-described process in whichthe channels 5 are widened until they go over into one another and thenflattened further as a result of etching, so that these may no longer bediscernible as parallel structures perpendicular to the longitudinaldirection of the edge 10. However, it is also possible to produce webs40 having edges 10 as are shown in FIG. 4, FIG. 5 or FIG. 6.

The abovementioned aspect ratio of web length to web width reflects thefact that the webs 40 are elements having a highly filigree structure.As an alternative or in addition, the web width 42 of such a web 40 canbe not more than four times the thickness of the glass element 1, forexample not more than twice the thickness of the glass element 1. In oneembodiment of the invention, the web width can even be smaller than thethickness of the glass element 1.

Regardless of the ratio of the width to the glass thickness of theaspect ratio, webs having a width of 400 μm or less, for example notmore than 200 μm, or even 100 μm or less, can also be produced accordingto the invention.

The example shown in FIG. 15 is an embodiment of the invention in whicha web 40 separates two openings 13 in the glass element 1. This isanother use of the invention, since it is associated with the removal ofinner parts to produce the openings 13, which in view of the sensitiveremaining thin web 40 would be difficult to achieve or not be able to beachieved at all by way other processes. In addition, comparativelyfracture-resistant edges 10 which stabilize the web 40 are at the sametime produced by way of the process owing to the substantiallyhemispherical structuring. The glass element 1 of course does notconsist only of the web 40, but instead the web 40 is joined to a basis43 in the form of a section of the glass element 1 having a greaterwidth. However, basis 43 and web 40 form only different sections of aone-piece glass element 1. In other words, the glass element 1 is amonolithic or one-piece part comprising the basis 43 and the web. In theexample shown in FIG. 15, the basis 43 is in the form of a frame and theweb 40 is joined at both ends to the frame-like basis 43. FIG. 16 showsa variant of the embodiment depicted in FIG. 15. In this variant, aplurality of webs 40 which run next to one another and at both ends goover into the likewise frame-like basis 43 are provided. As can be seenfrom this example, the webs 40 do not necessarily have to run in astraight line. The length of the web 40 is in such a case given by therespective curve length. Regardless of whether thin webs 40 are or arenot defined between the openings 13, the transverse dimension ofopenings 13, as can be produced by the above-described process and whoseedge 10 has substantially hemispherical depressions 7, for example atleast 200 μm, for example at least 300 μm. For example, a glass element1 having a plurality of circular openings 13 which are distributed overthe glass element and have a diameter of at least 200 μm or more can beproduced for various applications.

FIG. 17 shows still another variant. In this variant, the webs 40 goover into the basis 43 on only one side, so that the webs 40 have onefree end.

FIG. 18 and FIG. 19 show two further electron micrographs of the edge 10of a glass element 1. Here, FIG. 18 shows the edge 10 over the fullwidth of the glass element 1. FIG. 19 shows the edge 10 in a greaterenlargement at the transition to one of the side faces 2. The edge 10was produced as described above by the channels 5 being widened duringetching to such an extent that they join and form a continuous edge, sothat a part can be detached from the glass element 1. The channels 5have been flattened during the course of etching, so that an essentiallyflat edge 10 which has a plurality of adjoining, rounded, substantiallyhemispherical depressions 7 is obtained. As can be seen from FIG. 19,the depressions 7 are here too separated by ridges 70 which formapproximately polygonal delimiting lines 71. It is particularlyconspicuous in the micrograph of FIG. 18 that the edge 10 runs in astraight line perpendicular to the side faces 2, 3 and also essentiallyperpendicular to the side faces. Likewise, the transition from the edge10 to the side faces 2, 3 is virtually not rounded. The perpendicularcourse corresponds to the large angle of taper of the channels 5 of theembodiment shown in FIG. 6. The shape of this edge 10, as is alsosuitable for the webs 40 or for internal contours or as delimitation ofopenings 13, can be characterized by way of the abovementionedproperties as follows: the inclination or the angle formed by the edgearea with the adjoining side face 2, 3, is at least 85° in the half ofthe edge area adjoining the side face. Thus, the edge area 10 runsessentially at right angles to the side faces 2, 3, with a deviation ofnot more than 5° from a right angle.

As can also be seen in the example of FIG. 19, the transition region inwhich the inclination of the edge 10 goes over into the adjoining sideface 2 is narrow and of the order of magnitude of the dimension of thesubstantially hemispherical depressions 3. In one embodiment, theaverage edge radius at the transition from the side face 2, 3 to theedge 10 orientated essentially perpendicularly to the side face 2, 3 istherefore not more than 10 microns.

The edges 10 produced according to the invention are generallycharacterized, due to the substantially hemispherical depressions 7, byhigh strength and favourable statistical parameters, especially a highWeibull modulus. This can be advantageous in the case of fragileelements having edges such as the webs 40 shown in FIG. 15 to FIG. 17.In general, without being restricted to the examples presented, edges 10produced according to the invention with substantially hemisphericaldepressions 7 can have an average fracture strength of at least 200 MPaor even at least 300 MPa. This value is the tensile stress which occursat the transition from the edge 10 to the side face under flexuralstress and at which on average a fracture occurs. The Weibull modulus ofthe Weibull distribution of the tensile stress values for a fracturetest and fractures extending from the edge 10 can, according to analternative or additional embodiment, have a value of at least 5.5.These values apply both to the edges 10 having still visible channels 5,i.e. as per the examples of FIG. 4 to FIG. 7, and to edges 10 whichhave, as shown in FIGS. 18 and 19, no discernible channels 5.

Due to high stability and strength of the edges produced according tothe invention, the invention is suitable for complex and fragilestructures which are not producible by using other processes. Theretobelong also non-symmetrical structures with thin and/or long webs.However, at the same time, it was also ascertained that the stability ofthe products considerably depends on the geometry. In more detail, itwas ascertained that it is more favourable to comply with a certaingeometric specification, in case of a structure which is held inopenings in the glass element, by one or more webs. A sufficientstability and manageability is ensured by this specification.Particularly, a glass element is provided for that purpose which has atleast two openings 13 such that a structure having at least one web 40is formed between the openings 13. In doing so, a parameter G may beassigned to the structure that is given by the relation

$G = \frac{l_{1}^{2}}{l_{2} \cdot b \cdot \sqrt[3]{h} \cdot N}$

In doing so, glass elements according to the invention may still berealized with well mechanic stability, if the parameter G is at least 10mm^(−1/3), for example at least 50 mm^(−1/3), for example 100 mm^(−1/3).Vice versa, it is sufficient, if the parameter is at most 400 mm^(−1/3),for example at most 300 mm^(−1/3), for example at most 200 mm^(−1/3).

The variable h in the above relation denotes the thickness of the glasselement 1.

For clarifying the parameters of the relation, FIG. 20 shows a glasselement 1 having a simple structure that, in this case, only comprisesone web 40 extending between two openings 13.

In the above relation, li denotes the longest edge length between twoadjacent contact points or contact regions 45 positioned along the edgeof the structure, of one or two different webs 40 with the glass element1. Therefore, this quantity denotes the arc length of the longest edgebetween two adjacent contact regions 45. The edges 46, 47 of the web 40may, as also shown by the example of FIG. 20, have different lengths,depending on forming. In case of the shown example, the edge 46 has agreater length than the edge 47. The parameter 11 here therefore is thearc length of that edge 46. The contact regions 45 are the transitionregions of the glass, at which regions the web 40 goes over into theglass surrounding the openings 13, or into the base 43, respectively. Inthat context, a contact region 45 is defined as circular region having adiameter of 1 mm, the circular region positioned at the web 40 such thatits border touches both edges of the web 40, therefore also the edges ofboth openings 13. In doing so, the position of the imaginary contactregion 45 may be determined for calculating the parameter G, by shiftingthe circular region from the base 43 towards the web 40. The position isachieved, if the region just totally fits onto the glass, and its bordertouches the edges of the openings. As a result, this relation and thegeometry according to the invention applies for webs having a minimallength of less than 1 mm.

The length 12 denotes the shortest straight-line distance of two contactregions 45 at the ends of the web 40. The edge-to-edge distance of thecircular contact region 45 is significant for both lengths l1 and l2. Incase of more than two contact regions 45, the paths of the lengths l1and l2 do not necessarily continue between the same contact regions 45.The double arrow delineated in FIG. 20 for denoting the length l2accordingly ends at the edges of the contact region 45.

The parameter b finally denotes the smallest distance of the openings 13from each other, along the web 40, or, with other words, the minimal webwidth.

Such a geometry, as afore-said described, is, with respect to strengthand manageability especially advantageous in connection with the formingof the edge, according to the invention, therefore with hemisphericaldeepenings. Such a geometry may nevertheless be used with differentlyformed edges.

In case of the shown example, only one single web 40 is present. Butalso a plurality of structures is possible which may be carried by morethan one web. In that context, it is important that, in that case, thepaths l1 and l2 may continue between different contact regions 45. Forevaluating the stability of a design, G therefore relates the longestpossible distance between two contact regions l1 to the shortestpossible connection l2 of two contact points. N≥2 principally appliesfor the number N of contact regions.

For the sake of further illustration, FIG. 21 shows a glass element withthree different structures 39. The upper structure 39 is circular andheld at three webs 40. The structure 39 in the mid of the glass element1 is also held at three webs 40, but has a rectangular form. Thelowermost structure 39 consists, similarly to the example of FIG. 20,only of a single web 40. This web, however, narrows towards the mid. Indoing so, the web width clearly narrows from a width of more than 1 mmto a web width less than 1 mm, in the mid. Accordingly, also the contactregions 45 are on the web 40, for calculating the parameter G, namelysuch that their border touch the edges of the web at the place, at whichthe distance of the edges falls below 1 mm.

By way of the two upper structures 39, it may be seen that the distancel2 and the arc length l1 between the contact regions 45 may becalculated at different webs. The longest edge length l1 between twoadjacent contact points positioned along the edge of the structure isrelevant for the parameter G. This is each delineated for bothstructures 39. In case of the example of the upper-most, circularstructure 39, in particular a shortest distance l2 between two contactregions 45 and a longest edge length between two other, adjacent contactregions 45.

In one embodiment of the invention, not depending on the morphology ofthe edges. a plate-like glass element having a thickness in the rangefrom 30 micrometres to 3 millimetres and two side faces 2, 3 facing eachother is accordingly provided, wherein at least two openings 13 areinserted in the glass element 1 such that the region of the glasselement 1 between the openings forms a structure 39 with at least oneweb 40 whose minimal width is less than 1 mm, wherein a parameter G isdefined for the structure, G given by the above-mentioned relation,wherein the parameter G has a value of at least 10 mm^(−1/3) and of atmost 400 mm^(−1/3), wherein l1 is the longest edge length between twocontact regions 45 being adjacent along the edge of one of the openings13, and l₂ is the length of the shortest possible straight-lineconnection between two contact regions 45, and wherein a contact region45 of a web 40 is each defined as a circular region of the glass element1, having a diameter of 1 mm, the circular region arranged at the web 40such that its border each touches the borders of both openings 13 at atleast one point, the intermediate range of the openings forming the web40, and wherein b denotes the minimal web width, h the thickness of theglass element 1 and N the number of the contact regions 45. Webs havinga minimal width of not less than 300 μm can be used, for thisembodiment.

Also in case of the above-described geometry of a glass element with oneor more webs, fractures at the web may easily occur during production.

It was furthermore ascertained that, when producing such products,rejects due to web fracture occur, to an increased degree. This riskparticularly exists with glass element whose openings are clearly largerthan the remaining webs.

When detaching the inner parts, the webs may twist in the glass elementand take damage, in doing so. This may be avoided by generally,additionally to the closed separation line, inserting auxiliaryintersections, or auxiliary lines, respectively, made of adjacent,filament-shaped damages which divide an inner part limited by the closedseparation line into smaller segments. In doing so, it was ascertainedthat can be advantageous, if an inner part is at least bisected, e.g.quartered, by way of an auxiliary intersection. FIG. 22 shows, as anexample, a glass element 1 before detaching inner parts 9. The glasselement 1 is prepared with two closed separation lines 8 made ofadjacent channels, wherein the later web 40 continues between thesections of the separation lines 8, facing each other. An auxiliary line80 is inserted, additionally to each separation line, the auxiliary linedividing the inner parts 8 into two segments 91, 92, and 93, 94, each.It is apparent to the skilled person that, if needed, also furtherauxiliary lines may be inserted. Furthermore, the separation line 8 andthe auxiliary line may be inserted in one single step, for example byguiding the laser beam in an eight-shaped line.

In a refinement, the auxiliary lines are selected with regard to courseand number such that the inner part 9 is divided into segments of themaximally 20-fold size, for example the maximally 10-fold size, forexample the maximally two-fold size of a web between two inner parts 9.In doing so, the size ratio is determined by the ratio of minimal webwidth to maximal diagonal of a segment. Accordingly, the maximally longdiagonal of a segment is therefore 20-times, for example 10-times, forexample two-times longer than the minimal web width.

While this invention has been described with respect to at least oneembodiment, the present invention can be further modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

List of reference numerals Plate-like glass element 1 Side faces 2, 3Channel 5 Opening of 5 in 2, 3 6 Substantially hemispherical depression7 Separation line 8 Inner part 9 Edge of 1 10 Flat edge section 11Opening in 1 13 Computer 15 Positioning device 17 Apparatus for laserprocessing 20 Focusing optics 23 Laser beam 27 Ultrashort pulse laser 30Filament-shaped flaw 32 Polymer layer 35 Opening in 35 36 Structure heldby web 39 Web 40 Length of 40 41 Width of 40 42 Basis 43 Contact regionof 40 45 Edges of 40 46, 47 Wall of 5 54 Longitudinal direction of 5 51Ridge between channels 5 52 Ridge 70 Polygonal delimiting line 71 Pointof impingement 73 Corners of 71 72 Auxiliary line 80 Segments of 9 91-94

What is claimed is:
 1. A method for producing a plate-like glasselement, comprising the steps of: providing the plate-like glass elementhaving a pair of side faces and an ultrashort pulse laser having a laserbeam and focusing optics; directing the laser beam of the ultrashortpulse laser onto one of said side faces of said glass element;concentrating the laser beam by said focusing optics to form anelongated focus in the glass element; producing at least onefilament-shaped flaw in a volume of the glass element by a radiated-inenergy of the laser beam, a longitudinal direction of which runstransverse to said one side face of said side faces, and the ultrashortpulse laser radiates in a pulse or a pulse packet having at least twosuccessive laser pulses to produce said at least one filament-shapedflaw, and, after introduction of said at least one filament-shaped flaw;widening said at least one filament-shaped flaw to form at least onechannel by exposing said glass element to an etching process whichincludes an etching medium which removes a glass of the glass element ata removal rate of less than 8 um per hour; and introducing rounded,substantially hemispherical depressions in a wall of said at least onechannel by said etching process.
 2. The method of claim 1, wherein apoint of impingement of the laser beam on the glass element is conductedalong a prescribed path, and a plurality of filament-shaped flawslocated next to one another on the path are introduced into the glasselement, and a plurality of channels located next to one another aresubsequently introduced by the etching process into the glass element,and the glass element is then parted along the prescribed path so as toform an edge having said channels that are open at the sides.
 3. Themethod of claim 2, wherein a diameter of said channels of said pluralityof channels is increased by the etching process until a glass betweenthe said plurality of channels is removed and said plurality of channelsjoin.
 4. The method of claim 2, wherein a closed separation line and atleast one auxiliary line made of at least one adjacent filament-shapeddamage is inserted which divide an inner part limited by the closedseparation line into a plurality of smaller segments which are limitedby said at least one auxiliary line and the closed separation line. 5.The method of claim 1, wherein at least one side face of said side facesof the glass element is provided with a polymer layer before irradiationwith the laser beam, which polymer layer is removed locally onintroduction of the laser beam but remains at regions which surround apoint of impingement of the laser beam and protects these regions duringthe subsequent etching process.
 6. The method of claim 1, wherein saidglass element includes a web located in between a pair of inner parts,said web is in the form of a maximally two-fold size web, and saidmethod further includes a step of dividing each said inner part, by atleast one auxiliary line, into a plurality of smaller segments of themaximally two-fold size web, wherein a size ratio is determined by aratio of a minimal web width to a maximal diagonal length of one of saidplurality of smaller segments.
 7. The method according to claim 1,wherein introducing rounded, substantially hemispherical depressions ina wall of said at least one channel by said etching process includesintroducing said substantially hemispherical depressions adjoining oneanother and having abutting concave roundings which form ridges.
 8. Themethod according to claim 7, wherein ridges forming polygonal delimitinglines of the depressions are produced by the etching process.
 9. Themethod according to claim 1, wherein a plate-like glass element with asilicate glass is provided having a content of alkali metal oxides ofless than 17 percent by weight such that the silicate glass has abasicity in the range from 0.45 to 0.55.
 10. The method according toclaim 1, wherein an opening is produced in said plate-like glasselement, the opening having an edge with substantially hemisphericaldepressions, and a transverse dimension of at least 200 μm.
 11. Themethod according to claim 1, wherein a plate-like glass element isprovided having a thickness in the range from 30 micrometres to 3millimetres, wherein at least two openings are inserted into the glasselement such that a region of the glass element between the openingsforms a structure with at least one web whose minimal width is less than1 mm, wherein a parameter G is defined for the structure, and G isdefined by:$G = \frac{l_{1}^{2}}{l_{2} \cdot b \cdot \sqrt[3]{h} \cdot N}$ whereinthe parameter G has a value of at least 10 mm^(−1/3) and of at most 400mm^(−1/3), wherein li is a longest edge length between a pair of contactregions being adjacent along an edge of one of said openings, and l₂ isa length of a shortest possible straight-line connection between saidpair of contact regions, and wherein each said contact region of arespective web is each defined as a circular region of the glasselement, having a diameter of 1 mm, and said circular region is arrangedat said at least one web such that each border of said circular regiontouches corresponding borders of both of said openings on at least onepoint, an intermediate range of said openings forming said at least oneweb, and wherein b denotes a minimal web width, h denotes a thickness ofthe glass element, and N is a number of said contact regions.